title: Polarization in a Rashba strip coupled with a spiral spin density wave.
abstract: The magnetoelectric effect in a Rashba strip is studied, which is coupled to a spiral spin density wave (SDW). The polarization, if it can be induced, must be perpendicular to the plane constructed by the helix axis and the wavevector of the SDW. With a gate voltage on the strip varied, the polarization fluctuates quickly and can be switched from a positive to a negative value or vice versa. Furthermore, reversing either the helix axis or the wavevector leads to the reversal of polarization. The main contributions to the polarization come from the eigenstates in the vicinity of the von Hove singularities. At half-filling, contributions from different eigenstates offset each other exactly. With the Rashba spin-orbit coupling increased, the averaged polarization displays an oscillatory behavior due to the spin precession, whereas with the exchange coupling increased, the averaged polarization increases first then decreases. Considering the size effect on the polarization, the spin precession length is an important characteristic length.
authors.affiliation: Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China. zyzhang@nju.edu.cn
authors.forename: Zhi-Yong
authors.initials: ZY
authors.lastname: Zhang
authors.forename: Lang
authors.initials: L
authors.lastname: Chen